1. Field of the Invention
The present invention relates to a semiconductor substrate called an SOI substrate or the like and a method of producing the same.
2. Related Background Art
There are known methods for producing the SOI substrate having a single-crystal semiconductor thin film in such a manner that an Si wafer as a first base is bonded to another Si wafer as a second base with an insulating layer being interposed therebetween and a part of the first base on the back surface side is removed to make the single-crystal semiconductor thin film transferred onto the second base.
Particularly, the methods utilizing a porous layer, described in Japanese Patent Publication No. 2608351 and U.S. Pat. No. 5,371,037, are excellent methods to obtain an SOI substrate with good quality.
Further, U.S. Pat. No. 5,374,564 also describes a method of producing an SOI substrate making use of a layer with microbubbles (porous layer) formed by execution of ion implantation of hydrogen ions and a heat treatment.
The inventor prepared SOI substrates according to the description of the above patents. The inventor then made an MOS transistor using these SOI substrates and found that in application of this transistor to a high-frequency circuit, more improvement was required in high-frequency characteristics of the transistor and the circuit.
An object of the present invention is to provide a semiconductor substrate that can be an SOI substrate suitable for production of a high-frequency transistor, at a high yield.
Another object of the present invention is to provide a semiconductor substrate having a semiconductor layer region comprising a single-crystal semiconductor through an insulating layer on a support substrate comprising a semiconductor,
wherein the support substrate has such a composition that a semiconductor surface portion immediately below the insulating layer is a semiconductor having a resistivity of not less than 100 xcexa9cm and/or such a composition that the support substrate has a region with increasing resistivity toward the insulating layer in the direction of thickness thereof, and to provide a production method thereof.
Still another object of the present invention is to provide a method of producing a semiconductor substrate comprising a step of bonding a first base comprising a semiconductor layer region to a second base and a step of removing the first base while leaving the semiconductor layer region on the second base,
wherein according to the composition of the second base, a magnitude relation is established between the concentration of an n-type impurity and the concentration of a p-type impurity in an atmosphere for carrying out the bonding step.
Another object of the present invention is to provide a semiconductor device formed in a semiconductor substrate having a semiconductor layer region comprising a single-crystal semiconductor through an insulating layer on a support substrate comprising a semiconductor,
wherein the support substrate has such a composition that a semiconductor surface portion immediately below the insulating layer is a semiconductor having a resistivity of not less than 100 xcexa9cm and/or such a composition that the support substrate has a region with increasing resistivity toward the insulating layer in the direction of thickness thereof.
A method of producing a semiconductor substrate according to a preferred embodiment of the present invention is a method of producing a semiconductor substrate comprising a step of bonding a first base comprising a semiconductor layer region to a second base and a step of removing the first base while leaving the semiconductor layer region on the second base,
wherein the bonding step is carried out in an atmosphere in which the concentration of an n-type impurity is lower than the concentration of a p-type impurity, and wherein the second base is a base comprising a portion comprising an n-type semiconductor having a resistivity of not less than 100 xcexa9cm on the bonding surface side.
A method of producing a semiconductor substrate according to another preferred embodiment of the present invention is a method of producing a semiconductor substrate comprising a step of bonding a first base comprising a semiconductor layer region to a second base and a step of removing the first base while leaving the semiconductor layer region on the second base,
wherein the bonding step is carried out in an atmosphere in which the concentration of a p-type impurity is lower than the concentration of an n-type impurity, and wherein the second base is a base comprising a portion comprising a p-type semiconductor having a resistivity of not less than 100 xcexa9cm on the bonding surface side.
A method of producing a semiconductor substrate according to still another preferred embodiment of the present invention is a method of producing a semiconductor substrate comprising a step of bonding a first base comprising a semiconductor layer region to a second base and a step of removing the first base while leaving the semiconductor layer region on the second base,
wherein the bonding step is carried out in an atmosphere in which the concentration of a p-type impurity is lower than the concentration of an n-type impurity, and wherein the second base is a base comprising a portion comprising an n-type semiconductor having a resistivity of not less than 300 xcexa9cm and having an insulating layer formed on the bonding surface side.
A semiconductor substrate according to a preferred embodiment of the present invention is a semiconductor substrate having a semiconductor layer region comprising a single-crystal semiconductor through an insulating layer on a support substrate comprising a semiconductor,
wherein the support substrate has a region with increasing resistivity toward the insulating layer in the direction of thickness thereof near the insulating layer.
Another semiconductor substrate according to a preferred embodiment of the present invention is a semiconductor substrate having a semiconductor layer region comprising a single-crystal semiconductor through an insulating layer on a support substrate comprising an n-type semiconductor,
wherein the support substrate has a region with decreasing resistivity toward the insulating layer in the direction of thickness thereof and wherein the resistivity of a portion immediately below the insulating layer is not less than 100 xcexa9cm.
According to the present invention described above, the decrease of resistivity is restrained near the surface of the support substrate immediately below the insulating layer in the production of the SOI substrate.